The present invention relates to electrodes, and more particularly to disposable medical electrodes of the type employed in the transcutaneous monitoring of biological or physiological electrical potential associated with muscular activity.
In recent years, medical science has developed the art of transcutaneous monitoring to a rather high degree and for a variety of purposes. This type of monitoring is used to detect muscular activity of the heart muscle by use of electrical apparatus referred to in the art as an electrocardiograph (ECG). The resulting traces or electrocardiograms achieved with this procedure provide a diagnostic tool which enables the cardiologist to detect heart disease and general defects, etc. In addition to cardiomuscular applications, transcutaneous monitoring can be employed to indicate the degree of nerve blockage resulting due to anesthetization of a patient during surgery. In this regard, one set of electrodes are used to apply a controlled, low voltage potential to a particular muscle nerve, and a second set of electrodes may be used to monitor the resulting muscular contractions. These contractions are recorded on a electromyograph (EMG), with the resulting trace indicating the degree of effectiveness being achieved with the anesthetic.
The electrodes initially developed for ECG or EMG applications were reusable, and referred to as "permanent electrodes". These electrodes were of a type which utilized a non-conductive base that was applied to the skin either by means of suction cups or straps, with a metal terminal element housed within the non-conductive base and connected to the ECG or EMG apparatus via lead wires. To assure proper electrical contact, an electrolytic gel or paste was often employed in conjunction with the metal terminal. In many of these early designs, the terminals employed were either pure silver, German silver (pewter) or silver-plated metals or plastics, as it was found that silver provided superior results due to its tendency not to store an electrical charge. As can be appreciated, these permanent electrodes were rather expensive to manufacture. Also, the permanent type of electrode required that it be cleaned and disinfected after each use and before reuse. This procedure was time consuming such that disposable or single use electrodes were soon developed which out of necessity had to be of an inexpensive construction. Examples of several types of disposable electrodes can be found in U.S. Pat. Nos. 3,989,035 and 3,805,769.
These disposable electrodes typically included a support structure for the metal terminal element in the form of a relatively thin adhesively coated layer or disc of cellular foam, or in some applications, a thin microporous tape is used. The requisite metal terminal was provided by the employment of a two piece snap fastener engaged either directly through the foam or tape layer, or in some instances, the support arrangement was apertured with a second layer of impervious material overlying the aperture, and the snap fastener carried by said second layer. In conjunction with the snap fastener, a porous matrix was applied which in the case of a pregelled electrode, was impregnated with a quantity of gel, and a cover arrangement of some sort placed over both the gelled matrix and the adhesively coated surface of the support arrangement.
The snap fasteners which provide the electrical terminals for these prior art electrodes have proven to be both expensive, and a source contributing to inconsistent performance of the electrode. In this regard, the snap fastener component associated with the gelled matrix is of a two part construction, wih an inner element and an outer element, and is either totally or partially constructed of silver, stainless steel, nickel, or a silver-coated plastic or metal component. As such, the snap fastener is a relatively expensive component of the overall electrode construction, however, this design is tolerated as the snap fasteners lend themselves to the high speed automated construction of the electrode, necessary to achieve low cost production.
Further, it has been found that in use the snap fastener contributes significantly to the often erratic performance of the electrode. In this regard, the electrode is connected to the ECG apparatus by means of a lead wire having a female type snap connector on the end thereof engaged over the post or male component of the snap fastener. This connection provides considerable mass with respect to the remainder of electrode, such that patient movement results in alterations in the disposition of the electrode terminal with respect to the skin of the patient. More specifically, any movement producing tension in the lead wires would tend to pull the electrode terminal away from the patient's skin, whereas if the patient should happen to roll over, the protruding nature of the snap fastener would cause the metal terminal to be forced inwardly toward the skin, all of which contributing to the production of rather inconsistent ECG traces. As a further problem, electrodes with projecting snap fastener type terminal means do not lend themselves to stacking, and must be handled carefully during shipping and storage. In this regard, any rough handling or compressing together of the electrodes will tend to squeeze the gel from the gelled matrix.
The electrode system and electrode design of the present invention, as illustrated and described hereinafter, eliminates the need for the snap fastener as a component of the terminal means. Further, the present design achieves elimination of the snap fastener component, in a manner which results in improved performance, in that stability of the terminal position vis-a-vis the patient's skin is attained. Still further, this improved electrode design lends itself readily to automated assembly, and is usable with an overall system that envisions further improvements in the manner of connecting the electrode to the lead wire extending from the ECG or EMG apparatus.
More specifically, the electrode designs of the present invention utilizes a terminal arrangement provided by a pattern printed with conductive ink on a sheet of stable, semi-flexible, plastic-like material. The term "semi-flexible" is used with respect to the terminal bearing sheet for purposes of description, in that said sheet must be capable of slight flexure, yet must be relatively stiff or rigid, so as to resist any stretching or permanent deformation during use. Should stretching or deformation occur, this would result in fracture or interruption in the continuity of the printed conductive pattern, and thereby destroy its effectiveness as a conductive element. It has been found, that a relatively thin, clear, plastic-like film such as that sold under the trade name "MYLAR", is satisfactory for this purpose.
Looking to the overall basic construction, the electrode design of the present invention utilizes a support arrangement or layer which may be fabricated from a relatively thick, closed cell foam material of various types widely known in the trade, with one side of the foam support layer coated with a standard medical grade adhesive for securing or adhering the electrode to the skin of the patient. The support layer is apertured and the semi-flexible plastic-like terminal bearing sheet is affixed to the side of the support layer opposite that upon which the adhesive is applied. In this regard, the plastic-like sheet is positioned with the side having the conductive ink pattern thereon facing the support layer, with the terminal portion of said conductive ink pattern aligned with the associated aperture. Preferably, the conductive ink pattern also includes a conductor portion extending away from the area of the aperture, to which a lead wire is connected. The aperture in the support layer and the overlying plastic-like sheet material serve to define a well or chamber in which is disposed a porous or reticulated matrix, such as may be provided by a sponge-like plastic-like material, many versions of which are well known in the art. The porous matrix, or "gel pad" as it is often termed, is impregnated with a quantity of electrolytic gel, also of known formulation. A suitable easily removable cover arrangement overlies the adhesive coating on the support layer and the gel pad to prevent deterioration of the gel during storage.
The use of the semi-flexible terminal bearing sheet provides a relatively low mass terminal arrangement, which in use achieves a constant, stable positioning of the terminal means with respect to the skin of the patient. That is to say, the terminal portion will be spaced from the patient's skin, with the intermediate space filled by the electrolyte gel and the gel impregnated pad or matrix. This spacing is referred to in the art, and hereinafter, as the "gel column". More specifically, due to the low mass of the terminal arrangement provided by the conductive pattern on the sheet and the manner of connection of the electrode to the ECG apparatus, any patient motion, rolling over of the patient, or any tension on the ECG lead wires will not affect gel column stability to a great extent. Thus, the present design provides an inexpensive, disposable electrode capable of attainment of a consistent, highly accurate trace from the ECG apparatus.
As mentioned above, the manner of connecting the electrode to the ECG apparatus lead wire as contemplated by the present invention is also of significance, and contributes to the overall effectiveness of the electrode system. In both the single terminal and multi-terminal designs illustrated and to be discussed, the lead wires are connected at areas remote from the terminal portion. In one preferred, disclosed embodiment, the plastic-like, semi-flexible terminal bearing sheet includes a tab segment which is free of connection or adherence to the underlying support layer. The conductive pattern printed on said semi-flexible plastic-like sheet includes a conductor portion extending along this tab segment, such that the tab may be inserted within an electrical connector affixed to the end of an ECG lead wire. As will be discussed, the construction of the connector and the tab segment are such that they serve to isolate any stress or strain from the area of the terminal portion, which might affect the gel column.
A further aspect of the present invention and one most particularly applicable with respect to the single terminal electrode design discussed above, is the manner by which the design lends itself to automated fabrication. In and of itself, automated fabrication of an electrode is not novel, one such method of being illustrated and described in the aforementioned U.S. Pat. No. 3,805,769. The present invention, however, contemplates a novel method of assembly that is particularly advantageous with respect to the single terminal design as disclosed herein and other existing or possible future electrode designs.
In addition to the single terminal type of construction discussed above, the invention also contemplates various forms of multi-terminal assemblies, one of which is illustrated in the drawings and discussed in detail hereinafter. With the illustrated, contemplated design, a plastic-like, semi-flexible terminal bearing sheet is employed to join together two similar shaped support layers, each having one or more apertures therein with a terminal element on said sheet aligned with each aperture. With this arrangement, the semi-flexible sheet not only carries the terminal means, but acts as a hinge or connection between the respective support layer to provide an integral yet articulated assemblage. As will become apparent from the discussion to follow, this design is extremely advantageous with regard to both use of the multi-terminal assembly, its manufacture, and packaging thereof.
The present invention is possessed of numerous features and advantages, in addition to those discussed specifically above. It is believed that these features and advantages will become apparent from the detailed description of the invention which follows, taken in conjunction with the accompanying drawings which form a part of said description.